Membrane-associated, FAD-dependent malate:quinone oxidoreductase of the MQO family. Mqo1 catalyzes oxidation of (S)-malate to oxaloacetate while reducing a respiratory quinone, linking the malate/oxaloacetate step of the tricarboxylic acid cycle to the quinone pool of the aerobic electron transport chain. It is one of three MQO paralogs in Pseudomonas putida KT2440, so its exact paralog-specific physiological contribution is unresolved, but its domain architecture, HAMAP annotation, and orthology support a core role in respiratory malate oxidation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0006099 tricarboxylic acid cycle | IEA GO_REF:0000120 | ACCEPT | Summary: Correct process annotation for an MQO enzyme catalyzing the malate-to-oxaloacetate step of the TCA cycle using a quinone acceptor. Reason: UniProt/HAMAP annotates Mqo1 in the tricarboxylic acid cycle, specifically oxaloacetate formation from (S)-malate by the quinone route. The OpenScientist report independently supports this as the primary metabolic context for Q88PU7, while noting that the specific division of labor among mqo1, mqo2, mqo3, and NAD-dependent mdh is not experimentally resolved. |
| GO:0008924 L-malate dehydrogenase (quinone) activity | IEA GO_REF:0000120 | ACCEPT | Summary: Correct core molecular function for Mqo1, matching EC 1.1.5.4 and the UniProt catalytic activity. Reason: Q88PU7 is a HAMAP MF_00212/Pfam Mqo protein annotated as malate:quinone oxidoreductase, with the reaction (S)-malate + quinone = quinol + oxaloacetate. The deep-research report finds strong family-level biochemical and orthology support for this MQO assignment. |
| GO:0016614 oxidoreductase activity, acting on CH-OH group of donors | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: True but broad parent of the specific malate:quinone oxidoreductase activity. Reason: The enzyme is an oxidoreductase acting on the CH-OH group of malate, but GO:0008924 captures the specific substrate and quinone acceptor. This parent term is retained only as non-core background. |
| GO:0047545 (S)-2-hydroxyglutarate dehydrogenase activity | IEA GO_REF:0000118 | REMOVE | Summary: Electronic over-propagation from the PANTHER L-2-hydroxyglutarate dehydrogenase family name; not supported for this MQO. Reason: UniProt's curated catalytic activity for Q88PU7 is malate:quinone oxidoreductase, not (S)-2-hydroxyglutarate dehydrogenase. The protein carries MQO/HAMAP/Pfam evidence and the OpenScientist report supports L-malate oxidation to oxaloacetate with quinone as acceptor. No gene-specific evidence supports a 2-hydroxyglutarate substrate assignment, so this TreeGrafter annotation should be removed. The comparator confirms a graft artifact rather than a genuine second activity. The characterised E. coli malate:quinone oxidoreductase Mqo (P33940) carries GO:0008924 by IDA and has no (S)-2-hydroxyglutarate dehydrogenase annotation at all, while Q88PU7 carries the MQO-specific InterPro IPR006231, Pfam Mqo and HAMAP MF_00212 signatures rather than the L2HGDH ones that give PANTHER PTHR43104 its name. The substrates differ in carbon skeleton, C4 malate versus C5 2-hydroxyglutarate, so the term asserts a reaction this protein is not built to perform. |
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Download this section (compressed HTML)Q: Which of the three P. putida KT2440 MQO paralogs is the dominant malate:quinone oxidoreductase under organic-acid and gluconeogenic growth conditions?
Experiment: Purify recombinant Mqo1 and measure FAD content, L-malate kinetics, and quinone specificity using physiological ubiquinone analogs to confirm strict MQO activity and exclude 2-hydroxyglutarate dehydrogenase activity.
Experiment: Build single and combined mqo1, mqo2, mqo3, and mdh mutants and compare growth and flux on malate, succinate, acetate, and glucose to resolve paralog-specific contributions at the malate/oxaloacetate node.
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